Oxide particles have characteristic features, such as UV-absorption properties and near infrared ray reflection properties, which can be changed depending on the selection of a type of metal or metalloid element contained in the oxide particles. Thus, the oxide particles have been used in a wide range of fields, including cosmetics, such as sunscreen agents, lipsticks, and foundations; building materials, such as materials for exterior walls and signboards; or paints used for vehicles and glasses. Furthermore, when the intended use of oxide particles is of being applied to the human body, like cosmetics, the properties of beauty, texture, and safety are extremely demanded. In the case of using oxide particles in materials, such as materials for exterior walls and signboards or paints used for vehicles or the like, the demand for design properties, such as vividness and color aesthetic appearance, is also very high.
For this reason, there have been proposed a method for enhancing the properties of oxide, such as iron oxide and zinc oxide, including color characteristics, UV-absorption properties, and infrared ray reflection properties, by the process of atomizing the oxide (See, for example, Patent Literature 1 and Patent Literature 2) or the process of producing oxide using a plurality of elements other than iron or zinc (see, for example, Patent Literature 3 and Patent Literature 4).
However, although the transparency of fine particle dispersion can be improved by atomization, it is difficult to control their reflectance, transmission/absorption properties, color characteristics including hue and color saturation, and the like. In a complex oxide formation, furthermore, the properties of oxide largely change depending on the kinds of metals to be combined, causing in particular a difficulty of controlling the color characteristics of the oxide. These facts therefore make the properties of oxide particles difficult to be delicately controlled in a precise manner.
Patent Literatures 5 and 6, in which the inventions thereof are disclosed by the present inventors, disclose a method for producing uniform oxide nanoparticles by the process of precipitating various nanoparticles of an iron oxide and the like between two processing surfaces being capable of approaching to and separating from each other and rotating relative to each other. However, these patent literatures do not describe the method for manufacturing oxide with the objective of controlling the color characteristics of the oxide. In other words, Patent Literature 5 describes the separate formation of oxide and hydroxide, while Patent Literature 6 describes the manufacture of uniform oxide.